The proposed study investigates the role of sentence level fundamental frequency (F0) variation in speech intelligibility for persons with dysarthria associated with idiopathic Parkinson's disease (PD). It is of interest to know how prosody contributes to speech intelligibility deficits in developing an acoustic-phonetic model of speech intelligibility in dysarthria. The effects of segmental and suprasegmental variables on speech intelligibility have been addressed independently; however, few studies have been directed toward studying the interaction of segmental and suprasegmental variables and their effects on speech perception. Prosodic impairment, such as difficulty producing F0 variability across an utterance, may reduce the salience of acoustic cues to segment identity and have a detrimental effect on speech intelligibility. The primary aim of the proposed study is to look at changes in segment perception as a result of modification of the F0 contour. The study uses a speech resynthesis program that allows the investigator to modify F0 contours at the sentence level without affecting the timing and formant characteristics of the utterance. It is hypothesized that flattening of the F0 contour will increase segmental error rates, particularly for vowels. Enhancing the F0 contour to include the peaks and valleys typical in normal speakers will decrease segment error rates.